This invention relates to a method for installation of a cured in place liner into an existing conduit by air inversion of a resin impregnated liner with an apparatus having a low friction seal between the everting liner and a gland. The resin may be cured with continuous flow-through steam without loss of pressure and to the apparatuses for practicing the method. The method and apparatuses are particularly well suited for lining small to medium diameter conduits.
It is generally well known that conduits or pipelines, particularly underground pipes, such as sanitary sewer pipes, storm sewer pipes, water lines and gas lines that are employed for conducting fluids frequently require repair due to fluid leakage or deterioration. The leakage may be inward from the environment into the interior or conducting portion of the pipelines. Alternatively, the leakage may be outward from the conducting portion of the pipeline into the surrounding environment. In either case, it is desirable to avoid this leakage.
The leakage may be due to improper installation of the original pipe, or deterioration of the pipe itself due to normal aging or to the effects of conveying corrosive or abrasive material. Cracks at or near pipe joints may be due to environmental conditions such as earthquakes or the movement of large vehicles on the overhead surface or similar natural or manmade vibrations, or other such causes. Regardless of the cause, such leakage is undesirable and may result in waste of the fluid being conveyed within the pipeline, or result in damage to the surrounding environment and possible creation of a dangerous public health hazard. If the leakage continues it can lead to structural failure of the existing conduit due to loss of soil and side support of the conduit.
Because of ever increasing labor, energy and machinery costs, it is increasingly more difficult and less economical to repair underground pipes or portions that may be leaking by digging up and replacing the pipes. As a result, various methods had been devised for the in place repair or rehabilitation of existing pipelines. These new methods avoid the expense and hazard associated with digging up and replacing the pipes or pipe sections, as well as the significant inconvenience to the public. One of the most successful pipeline repair or trenchless rehabilitation processes that is currently in wide use is called the Insituform® Process. This Process is described in U.S. Pat. Nos. 4,009,063, 4,064,211 and 4,135,958, all the contents of which are incorporated herein by reference.
In the standard practice of the Insituform Process an elongated flexible tubular liner of a felt fabric, foam or similar resin impregnable material with an outer impermeable coating that has been impregnated with a thermosetting curable resin is installed within the existing pipeline. Generally, the liner is installed utilizing an eversion process, as described in the later two identified Insituform patents. In the eversion process, radial pressure applied to the interior of an everted liner presses it against and into engagement with the inner surface of the pipeline. However, the Insituform Process is also practiced by pulling a resin impregnated liner into the conduit by a rope or cable and using a separate fluid impermeable inflation bladder or tube that is everted within the liner to cause the liner to cure against the inner wall of the existing pipeline. Such resin impregnated liners are generally referred to as “cured-in-place-pipes” or “CIPP liners” and the installation is referred to a CIPP installation.
The CIPP flexible tubular liners have an outer smooth layer of relatively flexible, substantially impermeable polymer coating the outside of the liner in its initial state. When everted, this impermeable layer ends up on the inside of the liner after the liner is everted during installation. As the flexible liner is installed in place within the pipeline, the pipeline is pressurized from within, preferably utilizing an eversion fluid, such as water or air to force the liner radially outwardly to engage and conform to the interior surface of the existing pipeline.
Typically, an eversion tower is erected at the installation site to provide the needed pressure head to evert the liner or a bladder. Alternately, an eversion unit as shown and described in U.S. Pat. No. 5,154,936, U.S. Pat. No. 5,167,901 (RE 35,944) and U.S. Pat. No. 5,597,353, the contents of which are incorporated herein by reference. Cure may be initiated by introduction of hot water into the everted liner through a recirculation hose attached to the end of the everting liner. Inversion water is recirculated through a heat source such as a boiler or heat exchanger and returned to the inverted tube until cure of the tube is complete. The resin impregnated into the impregnable material is then cured to form a hard, tight fitting rigid pipe lining within the existing pipeline. The new liner effectively seals any cracks and repairs any pipe section or pipe joint deterioration in order to prevent further leakage either into or out of the existing pipeline. The cured resin also serves to strengthen the existing pipeline wall so as to provide added structural support for the surrounding environment.
The eversion tower, which was time consuming to construct, caused workers to be 30 feet above the ground often near trees and electrical wires. This method was improved by an apparatus, which allowed Insituform to create a hydraulic head by the use of a sphincter valve. The tube was fed into the top of the apparatus and pulled through the sphincter valve by pressurized water below the valve. The pressurized water applied a force on the nose of the tube causing it to invert into the pipe being rehabilitated. These apparatuses for the rehabilitation of small diameter pipe have been in use for about fourteen years.
The major disadvantage to the use of these apparatuses with water is the quantity and availability of the inverting water. Water must be heated typically from 55° F. to 180° F. in order to affect the cure, and then cooled by the addition of more water to 100° F. before being released to an acceptable disposal system.
This disadvantage may be overcome by using air in lieu of water to create the inverting force. Once the impregnated tube is fully inverted, it then can be cured with steam. Although water is necessary to produce steam, the quantity of water in the form of steam is only 5-10% of that required for water inversion, cure and cool down. This means that steam can be used even if water is not readily available on site. This drastic reduction in the quantity of water is the result of the higher energy available from one pound of water in the form of steam versus one pound of heated water. One pound of steam condensing to one pound of water gives off approximately 1000 BTUs while one pound of water gives off only one BTU for each degree in temperature drop. This reduced water requirement plus virtual elimination of the heat up cycle greatly reduces cure cycle and installation time.
With this apparent advantage in using air inversion and steam cure why has the industry been slow to abandon water inversion and hot water cure?
When water is used to invert the resin-impregnated tube, the uninverted portion of the tube from the inverting nose to the inverting apparatus is buoyed up by a force equal to the quantity of water displaced by the tube. In the case of CIPP tubes, this mean the effective weight of the tube is substantially reduced, as is the force necessary to pull the uninverted tube forward to the inverting nose. When air is used to create the inverting force, the uninverted tube lies on the bottom of the pipe and the air pressure acting on the inverting nose of the tube must pull the full weight of the tube forward.
Three forces must be overcome to invert a CIPP tube no matter what is used to create the inverting energy. These forces are:
1. Force required to invert the tube (turn tube inside out). This force varies by tube thickness, material type and relation of tube thickness to diameter.
2. The force necessary to pull the tube from the inverting apparatus to the inversion nose.
3. The force necessary to pull the tube through the inverting apparatus.
Force number one (1) above is generally the same for both air and water inversions.
Force number two (2) varies greatly between air and water and can limit the length of air inversions. There is limit on how much pressure can be used to invert a tube without adversely affecting the quality of the installed CIPP tube and/or damaging to the existing conduit. Lubricant can be used for both water and air inversion to reduce the required pulling force.
Force number three {3) can vary based on the apparatus design. In most apparatus presently in use, the force required to pull the tube through the apparatus will increase when either or both forces one and two increase. This is caused by the fact that in order to increase available inversion energy, typical apparatus in use today restrict loss of pressurized fluid from the pressure chamber below the tube entry point into the apparatus and the cuff and banded end of the tube being inverted. This restriction is typically accomplished by increasing the air pressure in a pneumatic gland (i.e. Insituform's CHIP 10 Unit) or by using a gland that is energized by the inverting fluid (i.e. The Shooter cup seal). The movement inward in both cases is restricted by the gland material and compression of the inverting CIPP tube. This in turn causes an increase on the friction between the inverting CIPP tube and gland.
In view of these apparent benefits of steam cure compared to hot water cure, the use of steam has been proposed in view of the energy it carries. Air inversion of an inflation bladder and flow-through steam to cure has been disclosed in Insituform U.S. Pat. No. 6,708,728 and U.S. Pat. No. 6,679,293, the contents of which are incorporated herein by reference. The processes disclosed in these recently issued patents utilize pull in and inflate technology and are currently in use for small diameter liners. They provide advantages over water eversion for small diameters. Moreover, use of a puncturing canister disclosed in these patents is not suitable for medium and large diameter liners. Medium size liners are those between about 18 and 45 inches in diameter. Large diameters are those in excess of about 45 inches and larger in diameter.
Accordingly, it is desirable to provide an improved apparatus for an air inversion and porting assembly for flow through steam cure CIPP installation.